1. Field of the Invention
The present invention relates to a bag for wrapping food, in particular bread and similar bakery products having at least one window for observing the contents of the bag.
2. Prior Art
The purpose of food packaging is fundamentally to protect the product against drying out, loss of aroma and harmful external influences. It must also be harmless to health. In relation to the durability and freshness of bakery products such as bread, firstly the products must not dry out and secondly e.g. the crust of the bread must remain crisp.
Fresh bread and similar bakery products are usually packed by bakeries in sheets of paper or in bags of paper or plastic or a composite material thereof. With conventional packing materials so far it has not been possible to keep the bread fresh for more than two days. With paper wrappings the cut edge of the loaf becomes dry and hard after two days at the latest. In plastic wrapping however the moisture of the bread is retained but the crust absorbs the moisture and thus becomes soft and rubbery. A further disadvantage of a plastic wrapping is that is can be detrimental to the product image of a natural product such as bread.
A further requirement for packaging for bakery products such as bread, in particular for use in bakeries, is ease of handling. The bakery products must be able to be packed quickly without great complexity so that the customer can be served as efficiently as possible.
It can also be a requirement to pack bakery products, in particular bread, still warm directly after its removal from the oven. Normal packing materials, in particular of plastic, cannot be used for this as mould quickly develops when the goods packed are warm.
DE 197 12 052 C2 shows a foodstuff bag which is easy to handle while guaranteeing adequate conservation and freshness of food, in particular bakery products such as bread. The bag is made of a laminate material with at least one layer of a cellulose-containing material and a second layer of plastic, where the first layer has a specific weight of 15 to 40 g/m2 and the second layer a thickness of 6 to 20 μm, where the laminate material is perforated and the ratio of open area to closed area of the laminate material is between 1/50 and 1/250.
As well as ease of handling, a particular advantage of this bag is that it can actively breathe through the perforations of the laminate material. This allows an exchange of moisture between the inside of the bag and the environment. Firstly sufficient moisture can escape from the bag that for example the crust of the bread can emit the moisture absorbed by the inside of the bread. At the same time however the amount of moisture loss is so low that even after four days a cut loaf still has enough moisture for it to remain tasty for the consumer.
The ratio of open surface to overall surface of the laminate material, e.g. the selection of hole size and number of holes per area, can establish the moisture exchange between the bag interior and the environment. Thus with a small ratio of open area to overall area of the laminate material, the moisture transfer from the bag interior to the environment is low, whereas for a large ratio the moisture transfer is greater. Thus the properties of the bag according to the invention can be adapted optimally e.g. to different bread types—loaves with a hard or soft crust, softer or harder bread. With a correspondingly selected ratio of open area to total area of the laminate material, the bag can also be used for packing bakery products still warm from the oven e.g. bread, or for packing the cooled bakery products for sale.
The combination of a cellulose-containing layer with a plastic layer not only controls the moisture emission but also ensures protection from light. The cellulose-containing layer, where it is on the outside, feels more pleasant than a plastic layer and is easy to print.
The laminate material is also sufficiently tear-resistant and despite this has a minimum mass, so that the amount of packaging waste is very small if the bags cannot be reused. This bag can be utilised not only for keeping bakery products such as bread fresh, but also for other foodstuffs such as for example cut cold meat, fresh meat or fish.
The first layer of the laminate material is preferably formed of paper or cellulose. The plastic of the second layer preferably consists of a polyethylene such as in particular an LDPE (low density polyethylene) with a density of 0.915–0.925 g/cm3 or an LLDPE (linear low density polyethylene) with a density of 0.92–0.935 g/cm3. Relevant criteria for selection are essentially the tear resistance and heat resistance.
The plastic layer should be resistant to temperatures up to at least 120° C., in particular for bags for bread to be packed warm from the oven or similar, so that the bread or similar can be packed as early as possible after removal from the oven.
The first and second layers can be releasably connected together so that the laminate material can largely be separated into its components. In particular this gives advantages for recycling. The layers of the laminate material can however also be firmly connected together, for example if the plastic layer is vapour-deposited onto the cellulose-containing layer.
The bag can have at least one seam in its linear direction. The seam can be formed by sealing, welding or gluing the first and/or second layers. For example by welding or sealing the adjacent plastic layers, at the seam point the first layer of cellulose-containing material lying on top can also be connected with the second layer. Thus with otherwise releasably connected layers the stability and strength of the bag are guaranteed.
The laminate material lying overlapping at the base of the bag is preferably joined with a double fold. The first layers of the composite material lying folded an each other can then be glued together giving a firm connection, in particular with an otherwise separable laminate material.
For the bag known from DE 197 12 052 C2 perforations are preferred formed as holes with a mean diameter of 0.3 mm to 1.5 mm, preferably 1 mm. With this hole size effective protection of the food is guaranteed against light influences and soiling with simultaneous moisture exchange.